Abstract: A data transfer method of a magnetic recording/reproducing apparatus which makes it unnecessary to repeatedly stop and start a recording operation or a reproducing operation in spite of changes in transfer interval and density of data transmitted between a host computer and the magnetic recording/reproducing apparatus, and which shortens the waiting time of the host computer to a minimum. When data transferred from a host computer is stored in a buffer memory and then transmitted to a rotary head, the number of revolutions of the rotary head and the feeding speed of a magnetic tape are changed by a switch control portion based on the amount of data stored in the buffer memory and the rate at which the amount of data increases or decreases. It is thereby possible to perform continuous recording regardless of the amount and density of the transferred data.